1. Field of the Invention
The present invention relates to a dehydrating apparatus for dehydrating an aqueous sludge composition which can contain fats and proteins, and which is produced in installations for purifying waste water, and in particular to an agglomerator which can be employed in such a dehydrating apparatus.
2. Description of the Prior Art
In biochemical purifying installations the waste sludge is obtained as a so-called biomass which is substantially free of fat and has a relatively high ratio of proteins and minerals; in physicochemical purifying installations sludge is produced after adding chemicals which will give rise to a flocculation of soluble substances. Especially in slaughter houses, sludge is obtained which has a relatively high ratio of proteins and considerable quantities of fat.
The sludge obtained from installations for purifying waste water generally comprises a rather low dry substance ratio, e.g., ranging from 2 to 8%, so that it is uneconomical to sell the same as fodder, whilst dehydration by evaporation of the liquid present will be too expensive, as this will require too much energy.
Thus, processes and installations have recently been proposed for increasing the dry substance ratio. These processes consist of a thermal conditioning, freezing of sludge, a sieve belt press and decantation or centrifugation.
These processes provide positive results. Moreover, new processes have been developed for anaerobic fermentation of sludge, thereby forming methane gas and a new sludge occupying a much smaller volume.
It appears that the separate use of each of the aforementioned methods is less attractive from an economical point of view, as regards investment costs, use of energy and production costs.